Method of making stems for sealed electrical devices



A. J. WHITE METHOD OF MAKING STEMS FOR SEALED ELECTRICAL DEVICES Filed NOV. 27, 1937 lnv entov- Arthuryijvhite, JD W /(5. M

y His Attovney Patented Aug. 23, 1938 METHOD OF MAKING STEMS FOR- SEALED ELECTRICAL DEVICES Arthur J. White, Cleveland Heights. Ohio, assignor to General Electric company a corporation of New York Application November 21, m1. Serial N5. 1mm

3 Claims. 7 ((21. 176+!) which carry the exhaust tube and the lead-in wires upon which the energy translation elements such as the filaments or electrodes of electric lamps or similar devices are mounted, is to assemble a stem tube, an exhaust tube and the lead-in wires with the inner ends of the stem and exhaust tubes lowermost and substantially in line. The expression "inner end is used herein with reference to the stem tube to indicate that end of the said tubewhich extends into the envelope or bulb and in which the lead-in wires are sealed, while the expression outer end, indicates the end which is united to the bulb. The corresponding ends of the exhaust tube are similarly designated. The stem is gripped by a pair of jaws at a point adjacent to its upper or outer end while the exhaust tube is gripped by another pair of Jaws. The lower or inner ends of the exhaust and stem tubes are fused together at a point below the stem tube holding jaws and then compressed by clamping the fused glassaround the lead-in wires with another pair of jaws. This results in a "press portion consisting of a flat solid mass of glass at the inner end of the stem tube with the lead-in wires extending therethrough. Air pressure is then applied through the exhaust tube to blow a passage through the molten glass at an angle to the flat surface of the press portiom The exhaust tube communicates through this passage with the interior oi. the envelope when the stem is sealed thereto. This process is described in Patent No; 1,423,956, Mitchell and White.

In some instances it is very desirable to make the stem. as short as possible and in those cases the stem cannot be made short enough by the above-described process. The stem tube jaws cover a substantial length of the stem tube and are spaced from the inner or lower end of the stem a substantial distance to prevent the molten glass from sticking thereto. Moreover, the flat press portion extends longitudinally oi the stem tube a substantial distance and thus further adds to the length of the finished stem. It is therefore not feasible to make the stem shorter than about 26 mm. according to standard practice; and this is too long for many purposes.

' One of the objects of the present invention, therefore, is to provide a method for making a shorter stem than can be made according to prior standard practice. Another object is to provide a method 0i making stems. which is very simple and economical and which-will produce stems which are gas tight and substantially tree from strains. Other objects and. advantages of my invention will appear from the following description and from the drawing.

In the drawing. Fig. 1 is an elevation. in section, showing the assembly or the parts of a stem on a suitable holder or-head ,in accordance with my invention; Fig. 2 is a plan view obthe holder or head; Figs. 8 and 4 are views similar to Fig; 1 illustrating further steps in the manufacture oi. a stem; Fig. 5 is a plan view ot-the stem shown in Fig. 4; and Fig. 6-is a longitudinal sectional view of an electric discharge lamp having stems therein made in accordance with my invention;

Referring. to Fig. 1, the stem tube It is disposed on the upper end of the holder ll of a head in' an upright position, that. is, with the flanged end i2 thereof lowermost,-contrary to the usual present practice. The exhaust tube is is disposed concentrically within the said stem tube. being gauged at its lower end by the upper end of a tube M (Fig. 4). The said exhaust tube ll extends through a closely fitting opening it and an enlarged opening it in the holder H and througha tube i'l-w-hich supports the holder i I.

The exhaust tube I3 is preferably located so that its upper end is below the upper end of the stern tube III, as shown in Fig. 1, although it may be at the same level as the upper end of the stem tube. The lead-in'wires it-il extend through openings l 9-l8 in the holder ii and are gauged at their lower ends by a nut ll; screwed on the threaded lower end of thetube H.

With the parts oi the stem properly disposed, the head comprising the holder II is rotated and the upper end-oi the stem tube is is-heated by .a gas flame from a burner 2i, causing it to collapse about the lead-in wires ll-il and form a' solid mass oiplastic glass 22 (Fig. 3) which forms a comparatively thin layer over the upper end oi the exhaust tube l3 and closes it oil. While the glass mass 22 is still plastic, compressed air is blown through the exhaust'tube I! to form an opening or aperture 23 (Fig. 4) through said mass in axial alignment with the exhaust tube Air is also blown into the space between the exhaust tube It and stem tube is to round out the Joint therebetween. The stem is then preferably further heated by a soft flame in order to anneal the glass and prevent cracking thercot upon cooling.

The air for blowing out. the opening as and'tor rounding out the Joint between the exhaust tube II and stem tube It is introduced through the tube It (Fig. 4), some of the air going straight up through the exhaust tube It. Some of the air also passes through lateral openings 24 in thetube it, into a sleeve 25 surrounding the ends of tubes I4 and i1, thence into the said tube i'i around the exhaust tube ll, through opening ii and through openings 2628 (Fig. 2) at the sides of opening I! into the space between the exhaust tube It and stem tube iii. The sleeve 26 is held between nuts 21 and 21 threaded on the tubes i1 and i4 respectively. In order to prevent the stem from being blown upward of! the holder II, it is weighted down, for example, by a cylindrical member 28 which rests on a flange 2! on holder ii and has its upper end inwardly flanged at It. The flange Iii extends over and Just above the flanged end i! of the stern i0, thereby preventing it from being blown upward.

It will be noted that in the process described above the glass mass 2! is not compressed by clamping as is the usual practice. By fusing the upper end of the stem tube and permitting the glass to flow downward freely, the stem may be made quite short, for example 12 mm. in length or even a little shorter if desired.

During the collapse of the upper end of the stem tube iii, a thin coating of glass ti-H adheres to the lead-in wires iI-il. For mounting an electrode 82 (Fig. 6) on the said leads "-4., the said glass coating li-fl may be removed, by pinching for example, thereby exposing the portions of the said leads covered thereby which are clean and free from oxide so that the ends of the electrode I! may be readily welded thereto, the ends of said leads being trimmed of! if desired. The electrode I2 preferably consists of a coiled coil of tungsten wire coated with an electron emissive material such as barium and/or strontium oxide.

For making a tubular electric discharge lamp as shown in Fig. 6, the stem 33 made by the process described above, is sealed to one end of a tubular glass envelope N. The sealing-in is preferably performed by the method described and claimed in my co-pending application Serial No. 178,910, of even date, wherein the adJacent end of the flange I! of the stem and the end of the envelope N are held in abutting relation with a disc of carbon, for example, which is heated by induction so that the said ends of the flange and envelope are fused and sealed together by heat conducted from the said disc. The opposite end ofthe envelope it has sealed thereto a stem N which is made in the same manner as stem 83 except that the exhaust tube It is omitted. To complete the lamp shown in Fig. 8, it is exhausted through the tube II and is then iilled with a gaseous atmosphere comprising, for example, a filling of argon at a pressure of about 4 mm. and a small quantity of mercury, after which the ex-, haust tube is sealed. The inner surface of the envelope may be coated with a luminescent material such, for example, as zinc silicate, cadmium silicate, calcium tungstate, cadmium borate or zinc beryllium silicate.

What I claim as new and. desire to secure by Letters Patent of the United States is:

l. The method of making a stem for an electric lamp or similar device which comprises assembling a stem tube, lead-in wires, and an exhaust tube in a vertical position with the exhaust tube inside of the stem tube and the lead-in wires extending longitudinally of said tubes, fusing the upper end of said stem tube to cause it to flow freely downward and form a solid mass of glass inclosing a portion of said lead-in wires and forming a comparatively thin layer over the end of said exhaust tube to close it 01!, and delivering gas pressure through said exhaust tube to blow an aperture axially through said mass of glass.

2. The method of making a stem for an electric lamp or similar device which comprises assembling a stem tube, lead-in wires, and an exhaust tube in a vertical position with the exhaust tube inside of the stem tube, the upper end of said exhaust tube being located below the upper end of said stem tube and the lead-in wires extending longitudinally of saidtubes, fusing the upper end of said stem tube to cause it to flow freely downward and form a solid mass of glass inclosing a portion of said lead-in wires and forming a comparatively thin layer over the end of said exhaust tube to close it off, and delivering gas pressure through said exhaust tube to blow an aperture axially through said mass of glass.

3. 'The method of making a stem for an electric lamp or similar device which comprises assembling a stem tube, lead-in wires, and an exhaust tube in a vertical position with the exhaust tube inside'of the stem tube and the lead-in wires extending longitudinally of said tubes, fusing the upper end of said stem tube to cause it to flow freely downward along said lead-in wires and form a solid mass of glass inclosing a portion of said lead-in wires and forming a comparatively thin layer over the end of said exhaust tube to close it off, and delivering gas pressure through said exhaust tube to blow an aperture axially through said mass of glass, removing the thin coatings of glass on said lead-in wires above said mass of glass and welding the ends of an electric energy translation element to the thus exposed portions of said lead-in wires.

ARTHUR. J. WHITE. 

